Here are some random notes I'm keeping on a new approach for solving
backwards.

 === === === === 
|R..|... ... ...|
     === ===     
|y.. ... ... ...|
     ===     === 
|... .RS|...|g..|
                 
|... ... ...|b..|
             === 
|... ... ... ...|
 === === === === 

 === === === === 
|A..|.B. .b. .B.|
     === ===     
|aB. .b. .b. .B.|
     ===     === 
|a.C ..C|...|...|
                 
|a.. ... ...|...|
             === 
|A.C a.C a.. A.C|
 === === === === 

 === === === === 
|R0.|... ... ...|
     === ===     
|r1. ... ... ...|
     ===     === 
|r1. ...|...|...|
                 
|r1. ... ...|...|
             === 
|R1. r2. r2. R2.|
 === === === === 

 === === === === 
|...|... ... ...|
     === ===     
|F.. ... 4F. ...|
     ===     === 
|1.. 0..|4F.|...|
                 
|2F. 1.. 4F.|...|
             === 
|2F. 1.. 3F. 3F.|
 === === === === 

 === === === === 
|...|... ... ...|
     === ===     
|... ... ... ...|
     ===     === 
|1.. 0..|...|...|
                 
|... 1.. ...|...|
             === 
|... 1.. ... ...|
 === === === === 

 === === === === 
|...|... ... ...|
     === ===     
|... ... 3A. ...|
     ===     === 
|1.. 0..|3A.|...|
                 
|... 1.. 3A.|...|
             === 
|A.. 1.. 2A.2A..|
 === === === === 

 === === === === 
|3B.|6B. 6B. 5B.|
     === ===     
|3B. 4B. 4B. 4B.|
     ===     === 
|1.. 0..|5B.|...|
                 
|3B. 1.. 5B.|...|
             === 
|2B. 1.. B?? 6B?|
 === === === === 

 === === === === 
|...|... ... ...|
     === ===     
|... ... ... ...|
     ===     === 
|1.. 0..|...|...|
                 
|C.. 1.. 2C....|
             === 
|... 1.. ... ...|
 === === === === 

 === === === === 
|...|... ... ...|
     === ===     
|... ... ... ...|
     ===     === 
|1.. 0..|...|...|
                 
|2D. 1.. D..|...|
             === 
|... 1.. ... ...|
 === === === === 

 === === === === 
|2E.|5E. 5E. 4E.|
     === ===     
|2E. 3E. 3E. 3E.|
     ===     === 
|1.. 0..|4E.|...|
                 
|E.. 1.. 4E.|...|
             === 
|5E. 1.. 4E. 5E.|
 === === === === 

 === === === === 
|...|... ... ...|
     === ===     
|F.. ... 4F. ...|
     ===     === 
|1.. 0..|4F.|...|
                 
|2F. 1.. 4F.|...|
             === 
|2F. 1.. 3F. 3F.|
 === === === === 


 === === === === === === === === === === === === === === === ===
|2+* 2+* 2+* 2+* 1+*|7.* 5.* 5.* 5.* 8.* 8.* 7.*|6.* 6.* 4.* 5.*|
                                                     ===
|3.* 3.* 3.* 3.* 1.. 4.* 4.*|5.* 5.* 6.* 6.* 6.* 6.*|6.* 4.* 5.*|
     ===                 ===
|3.*|9.* 3.* 3.* 1.. 7.* 4.* 5.* 5.* 9.*|6.* 6.* 6.* 6.* 4.* 5.*|
                                     ===
|3.* 4.* 3.* 3.* 1.. 4.* 4.* 4.* 4.* 4.* 4.* 4.* 4.* 4.* 4.* 4.*|
                                                             ===
|3.* 3.* 3.* 3.* 1.. 3.* 3.* 3.* 3.* 3.* 3.* 3.* 3.* 3.* 3.* 2.*|
                         ===
|3.* 3.* 3.* 3.* 1.. 3.* 2.*|5.* 5.* 5.* 6.* 6.* 6.* 6.*|3.* 2.*|
 ===                                         ===         ===
|4.* 4.* 3.*|3.* 1.. 4.* 2.* 4.* 4.* 4.* 4.* 4.*|3.* 3.* 3.* 2.*|
             ===             === ===
|3.* 3.* 3.* 3.* 1.. 3.* 2.*|... ...|3.* 3.* 3.* 3.* 3.* 3.* 2.*|

|3.* 3.* 3.* 3.* 1.. 3.* 2.*|... ...|5.* 5.* 5.* 5.* 5.* 4.*|2.*|
                             === ===                     ===
|5.* 5.* 3.* 4.*|0+. 1.. 1+. 1+* 1.* 1.* 1.* 1.* 1.* 1.* 1.* 1.*|
                 ===     ===     ===                         ===
|5.* 6.* 3.* 4.* 6.* 6.*|7.* 2.* 7.*|5.* 6.* 5.* 6.*|7.* 2.* 8.*|
 ===                                                 ===
|9.* 9.* 3.* 4.* 7.* 7.* 7.* 2.* 7.* 5.* 9.* 5.* 7.* 9.* 2.* 9.*|
                             ===
|8.* 8.* 3.* 4.* 7.* 7.* 7.* 7.*|7.* 5.* 8.* 5.* 7.* 8.* 2.* 8.*|
     ===                                 ===
|9.* 9.*|3.* 4.* 4.* 4.* 4.* 7.* 4.* 4.*|7.* 5.* 7.* 8.* 2.* 8.*|

|5.* 5.* 3.* 4.*|7.* 7.* 7.* 7.* 7.* 5.* 7.* 5.* 7.* 8.* 2.* 8.*|
             ===
|8.* 8.* 3.* 8.* 7.*|6.* 6.* 6.* 6.* 5.* 6.* 5.*|7.* 8.* 2.* 8.*|
 === === === === === === === === === === === === === === === ===
|... ... ... ... ...|... ... ... ... ... ... ...|... ... ... ...|
                                                     ===
|... ... ... ... ... r.. .yo|... ... ... ... ... ...|.rs ... ...|
     ===                 ===
|...|.gt ... ... ... ... ... ... g.. .bt|... ... ... ... ... ...|
                                     ===
|... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ...|
                                                             ===
|... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ...|
                         ===
|... ... ... ... ... ... .bs|... ... ... ... ... ... ...|.go ...|
 ===                                         ===         ===
|... ... ...|.rc ... ... ... ... ... ... ... .yc|... ... ... ...|
             ===             === ===
|... ... ... ... ... ... ...|... ...|... ... ... ... ... ... ...|

|... ... ... ... ... ... ...|... ...|... ... ... ... ... Yys|...|
                             === ===                     ===
|... ... ... ...|.YT ... ... ... ... ... ... ... ... ... ... ...|
                 ===     ===     ===                         ===
|... ... ... ... ... ...|.bc ... .rt|... ... ... ...|.gc ... ...|
 ===                                                 ===
|... b.. ... ... ... ... ... ... ... ... ... ... ... ... ... ...|
                             ===
|... ... ... ... ... ... ... .ww|... ... ... ... ... ... ... ...|
     ===                                 ===
|... .ro|... ... ... ... ... ... ... ...|.bo ... ... ... ... ...|

|... ... ... .gs|... ... ... ... ... ... ... ... ... ... ... ...|
             ===
|... ... ... ... ...|... ... ... ... ... ... ...|... ... ... ...|
 === === === === === === === === === === === === === === === ===