In my understanding drawn from what I have read from many merits sources in many threads, they do not have the same smerit allocation, and some users' monthly smerits could be so much while others could be annoyingly low. The reason is best known to theymos, but upon request with evidence of usage of the ones you were given, I think he can adjust the allocation based on his discretion.

As for being a lifetime merit source, I think it is possible if you maintain a good membership/reputation and do not renege from the reason why you were given. But of course, if you are no longer active on the forum, what is your worth? For this, such a user's merit source status may be withdrawn.

There are other offences which may not be plain that could cost users their merit source status as well. So it could be slightly similar to that of the DTs but not as rampant as them.