As an update, some interesting facts that have been confirmed from my search through all the Rhodes production. My spreadsheet is coming together with a good range of serial numbers, date codes, and production info with picture backup to confirm, so hopefully in the coming year I'll have a good base by which we can see what is in each Rhodes:
1) From start to finish a Rhodes took roughly at least 3 months to make it out of the factory. On one particular Rhodes, The inside of the case is dated December 18th 1973, the harp start date of the Rhodes is 0474 (Jan/Feb), and completion date is usually 4 weeks later but roughly spans 2-10 weeks later.
2) Hybrid wood hammers are in a 2375 Rhodes, meaning the all plastic hammer transition was closer to Mid year 1975, around June.
3) All Mark IIs made in 1980 have wood keys. Wood keys on a Rhodes dated 0981, white plastic on a Rhodes dated 1881, plastic keys were introduced sometime after March 1981.
4) Beginning sometime in 1971, the Stage pianos were referred to on the badge as Mark 1A, Latest Mark 1A date I have is 0672. This means the 88 was introduced sometime after Feb 1 1972 as the name of models "stage 73" and "stage 88" had to be used to differentiate an 88 key set.
5) When 1970 stage pianos came out they used different rear leg ends where the crossbraces attach, compared to the standard set. Also used 3 hinges for the case lid on the back.
6) The 4 pin preamp and amp were used all the way up until late 1977, roughly October '77 around 40th week.
7) Not all Black grilled suitcase pianos have legs that fold out flush to the edge of the speaker cabinet. This was introduced sometime around 4078, Oct '78.
8 ) Not all 1973 Rhodes pianos had Full skirt Rounded Keycaps. They introduced the now-looking-yellow 2 piece caps very late 1973, earliest date of these keys for me is 4973 ~December.
9) Though I don't know what the initials TBJ stand for (or the purpose really, if it was for parts lists), it refers to the keyset model (seventy three, eighty eight, fifty four, etc). TBJ numbers are the same on all Mark I 73 keysets, whether it's a stage or a suitcase: 010254. Mark I 88 models have a different number: 010459. Then, Mark 2 introduced new TBJ numbers for 73 (017249), 88 (017250), and 54 (017281) keysets. If anyone can help me out with a TBJ number from a piano bass before 1979. Late piano bases labeled 23646TBJ.
10) Piano basses were still being sold in the Mk1 style when the Mk2 models were introduced. The earliest Mk2 I have on record is 4879. I have one bass confirmed dated 5079 that was completed (sold after) 20th week of 1980. I do have a strange PianoBass dated 2982 but it has a lot of red flags (gold "Rhodes" badge, red date, old fender rail logo) which means I can't confirm if it's legit or not.
The only point of discussion would be that the start date on the harp isn't the "Date" of a transition - for example, if the harp dated 1881 has white plastic keys, maybe the transition took place before18th week of 1981because it looks as though the factory built the chassis before the harp was started. However, In my opinion the transition date should really be according to the harp completion date, as we've seen rare cases where harps that are started say 1677 sit around for upto 6 months before they're paired with a box and completed in 4677. In this case, the start date shows it should have a 4pin suitcase amp, but when completed it was paired with a 5pin amp. The only problem is that completion dates are tougher to come by, so hopefully serial numbers will help here.
The only real challenge is to get everything all together onto one easy-to-read sheet or timeline. Hopefully when this spreadsheet is posted, there'll be no more buying "keys that don't match," or "Whoops the top I bought doesn't fit." Or having to ask an ebayer "What's the date code you only listed a serial number" and you'll be buying exactly the Rhodes you want.