A card with an expiry date will often be dated a little past the actual end of the status year to allow for new card being sent out if you requalify, and the card should give you higher benefits until its expiry even if you have dropped a status level. But a card without a date is not likely to be taken as a 'lifetime' card . Does it have a start date?

The various *A airlines usually put your status on the BP by cross-checking with the 'home' airline of your FPP. I imagine that part of the pre-joining period will have been spent getting this computer stuff in place. If TAM were a member and you were Gold when you booked then this status may have 'stuck' on the booking.

If not then a sufficiently confused or bored check-in agent might manually set the status to Gold, or grant you equivalent benefits, when reviewing your card.

Lounge access staff are usually far more on the ball about who to give access to, and I doubt you'd get past them.