Actually, hair loss, doesn't happen instantly so I don't really know what you mean
by after 6 months its over.
The folicle gets smaller and smaller under DHT action, more DHT and susceptibility to DHT (some are actually not susceptible to it at all) makes the folicle get smaller quicker (even in women, that's why many women have thin hair after menopause).
So, the recovery, its speed depends more on how small the hair shaft is when you suppress DHT and how susceptible you are to it. In my case, I've got very dense hair everywhere but my two temples which started to lose hair at about 18. So, I've got a 0.75x1 inch area on both sides with no recovery (not a very big area thank god) (I'm 40). But, elsewhere, from that area to the middle, a 0.75x1.5 inch area (Call it upper temples), where hair was lost gradually from 25-38, it has already half recovered in 2 years. Some of those hair, I couldn't see at all 2 years ago, and where almost an inch from my pre-HRT hairline. So, it seems, its not 6 months, it more.... It depends...
So, someone could be losing hair for a very long time, but still have salvageable hair if it hasn't become too small.
As for T not existing post testes being removed, it does exist, from the adrenals, like in women.
If your highly susceptible to DHT, you should continue using it even post SRS or your hair will thin out from the T -> DHT transformition of adrenal's T.
a general Anti-T, like spiro, serves another purpose post SRS, allows continued and quicker demasculinisation by blocking the adrenal T (specially good for those who do SRS 1 year after starting HRT).
Remember, we start with potentially a greater muscle mass and central fat deposit than women (both influenced by T), so we need all the help we can get getting it down faster.
