Many of them are HTL (inorganic) which is the entire point of M-Discs, using an inorganic instead of organic dye. There are LTH BD-Rs (organic dyes) which are shit, but any HTL one should work for medium term archival, and you can identify them in a disc reader software. Verbatim has a MABL BD-R thing too, which burns off metal instead of changing a dye.