If I remember correctly TPs only started in the 1990s didn't they? So the OP may find that he/she won't have quite as many as they may think.
Without digging out old statements and handbooks, I think it was either 1995 or 1996 that tier points were introduced.
BA did not offer any conversion for mileage based years to those who accrued a lot of BA flying time before tier points were introduced. Maybe they think we're all so old that we don't have much chance to use lifetime status!
