Well, just to let all of you know that I've managed to install all of the ECS vectors in my currently running game, a game that has been running for quite some years now - and I'm not speaking game years here...
And the solution; the "Cht: PurgeIndustries"! Thanks for pointing me to this one. I had no idea industry ID's - or houses for that matter - could still occupy an ID-list even after being removed from the newgrf.list! So again, a BIG thank you to all that has helped me with this, and especially Wally!

I appreciate it a lot! A surprise is heading your way!
Of course I didn't want to take any risks, especially not after reading about that "PurgeIndustry" stuff, so obviously I figured that "better safe than sorry", and deleted they were - ALL my industries everywhere! And no signs added! Those of you who have been following my INFRA-work knows all too well that my map has been a major construction site ever since I finished developing it in the Scenario Editor...

I need to relocate all my industries anyways after getting all these "new" industries... I'm sure all the local councilmen - and women - will be very pleased - as usual - to find my bulldozers working around the clock again, destroying and wrecking about...
I'm sure this was known by others before, but it's not possible to use MB's NewCargo along with ECS, but I'm known to "mix and match"...

...so it'll find its way into my game somehow, the graphics I mean...

The same goes for the OilFiredPowerStation, (whoever made that one), which I'm using for my BusDepot, but that doesn't really matter as I plan to make it modular instead!
The entire thing with Cht: PurgeIndustries" has made me wonder if the same issues with houses and industries also applies to stations. The reason be is that Wally seems to be able to load the CanadianStation Set, (with ALL those thousands of sprites), along with IndustryRenewal, while I'm only able to load the DutchStation Set along with my "Test Files", each of them providing 108 sprites, in total for the latter approximately 500 sprites! What was the station sprite limit again?