Unfortunately we do not have a forum like Järnvägshistoriskt Forum in The Netherlands.
What I see at Dutch forums is mostly chit-chat about present day railways.
That is why I do not visit them very much.
I had a look at 'skyscrapercity', but it is not for me. I do not think it can be compaired
to Järnvägshistoriskt Forum at all.

I contacted the person behind www.industriespoor.nl which is a site about the industrial railways in The Netherlands which has, over the years, gathered a lot of information on the subject.
He send me an article which was published in 1951. Go to page 367-369 in this link:
https://resolver.kb.nl/resolve?urn=MMUTRA03:004517023:00001
This article is partly about the three tankwaggons. The drawing is of the ASJ waggons.
The last photograph in the article is probably the same as the one in the 1950 catalogue with the number ASJ 25103.
The second last photograph is number 530303
It was part of the small serie of waggons NS 530302 - 530304 of the Koninklijke Nederlandsche Zoutindustrie at Hengelo. The assumption that it was near Roermond was not right.
Later on they got UIC1 numbers:
530302 became 21840705726
530303 became 21840705727
530304 became 21840705728.

All three were taken out of service (slopad) at the end of 1975/ beginning 1976.

If there is anything unclear, just let me know and I shell see if I can clear that up.