in some documentation Olivetti talks about an "E.G.C. Enhanced Color Graphics Controller" which should be the same DEB. I don't know if any board was actually marked EGC but it may be an older name. https://secure.corradoroberto.it/doc/olivetti/systems2/capa.pdf

The naming for that card is quite confusing, if you have a look on that capa.pdf, you can see that it would fit in M24 (and M21 but does not make sense here), M28, M240 and M280.

Additionally you also find the name "Video Enhancement Adapter" (VEA) for the GO329 in some technical documents for M24. So real Olivettians don't talk about "DEB" or "EGC" or "VEA", but about "GO329", this is more precise.

But as the GO329 has M21/M24 proprietary 16 Bit connector, it can not fit in M240, as it only has standard 8 Bit ISA like any other XT as well, and it can not fit into M28 and M280 as they are 80286 AT with standard 16 Bit ISA slot. If you have a look into cap2.pdf (M240), and cap4.pdf (M280) you also will not find any mention of the GO329 what is the trueth, as it does not make sense because of the slots. But you still find it in the cap3.pdf (M2, but there also it does not make sense.

But M240, M28 and M280 can support the 640x400x16 modes, without using the GO329 if they have the original OEC/OVC (EGA/VGA) cards. There are also monochrome/greyscale cards (OGC,PGC) which only support the 640x400 in monochrome, like M24 OGC card.