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The 15xx series (Blankenberge-Genk) trains are either formed of M6 double deckers (https://nl.wikipedia.org/wiki/M6_(spoorwegrijtuig)) or MS96 (EMU with "danish noses" very similar to the I11 coaches).
The 23xx series (Oostende-Brussel Airport via Kortrijk) can drop M6, MS80 and MS08.
The 28xx series (Knokke-Brussel Airport) is either M6 or MS80 with an odd MS96 thrown sometimes.
If you are interested in formations of specific trains, http://www.beluxtrains.net/ has the planned rolling stock for all belgish trains (also of earlier years) and at least the beta of the HyperRail app (https://play.google.com/store/apps/details?id=be.hyperrail.android) is capable of providing realtime information including formation and numbers (but the NMBS data feed is not too reliable).