I've had a few and I suppose that's possible, losing porosity that is. I have one that's gone sour and thought mb I accidentally let some cake build up cuz I haven't even smoke 20 bowls through it. Mb it's cuz the African meer is less porous, idk.
It's a Kiko Tanganika meerschaum lined, leather wrapped briar pipe which I bought as an unsmoked estate pipe. So even if i don't smoke It it's a piece of history and I like looking at it and contemplating the ills of colonialism.
Anyway, my final prognosis is I personally am not messing with any more meer lined pipes. Btw there often pressed meerschaum and really I see them as more of a novelty. If a anyone swears by them I'd love to hear from them.
But from now on if I want meerschaum I will get an actual block meerschaum pipe. Unsmoked and with a push pull tennon.