HI guys,
It is a safe bet that the changes bought about in the middle of 1980 was caused from the factorys view of importing into the USA ...which began in 1982.
Fender USA also approached Tokai around the same time (1980) to produce the new Fender Japan range hence the change in 1981 to Fender-spec Springys and the gradual change in logo and serial numbers. The contract eventually went elsewhere, but the headstock re-shape didn't start till late 1982. The USA catalogs in 1983 and 1984 have altered headstocks with TST-56, TST-62 and TTE-52 model numbers, even though the rest of the World markets continued to receive the regular headstock shape. 1985 bought a Model name change to AST instead of TST.
I would think that Tokai, hearing what was happening to Ibanez USA, brought in the changes to dodge a potential bullet before taking on the American market.
America was a big market for Tokai in the early-80s. I remember trying to order ES-100s - only to be told that the whole ES-100 production for the next Year had already been ordered by USA
regards
Peter Mac