I take my 30s to a bilk seller. Last time I had them filled they had 1 month left before needing re-cert. They told me they would do it when I brought them back next time. I think he said $12. Of course that will be like 3 years. We just don't use much propane.
And yes they check dates. Not sure if LP tanks are the same as SCUBA, but SCUBA tanks are most likely to fail during refill.
I also have 2 other 30s I keep in the shop (bought from Amazon). He did miss them being new but was glad I told him since they have to be purged.
