The FIA papers I have (FIA No. 1286 dated 25.03.64) have a sheet attached which refer to FIA Bulletin No. 250. This states:
'BMW 1800Ti
Homologations-Nr. 1286 von 1964). Es wird bestaatigt, daB*ias Modell "TiSA" nicht homologiert wurde.'
At the bottom of the sheet, which is not a good copy (hence the missing letter in the above quotation), is the caption 'ONS-Vitteilungen 11-12/90'
I don't speak German so make of that what you will.
On the Motorbase website there is little reference to the BMW 1800 TiSA but there was a note thatone was sold by Coys in August 2009 described as one of the original 200 built by the factory and this particular one was built in 1965.