works, diversions, temporary measures-these can be planned and as its DE=Germany will be in some giant planning book, will not be put into the online Fahrplan (timetable) untill a day like 7-10 before and even then often not-except as a footnote.Daniel should know this as NS does the same. I guess they simply lack the staff to put in all those changes online.
NS is always late with this indeed (their page with planned works on the ICE International route is actually empty currently), but the
DB page with planned works is usually up to date quite far in advance.
The journey planner is also up to date at least 2 months in advance, it might however that you can't book tickets to the section where works are ongoing. I had that when booking the return leg of my holiday: the actual timetable for that specific day was already available including a diversion, but I couldn't book to Cologne. Booking to Düsseldorf worked fine however so I opted to change there instead.
I'd mistaken however as in the period I mentioned the trains are being diverted within Germany reading the announcement more carefully. The diversions via Venlo where known that far in advance that they're apparently already included in the standard timetable.
Side note: as you plan a change in Airport BHF-this likely means to get into the 1/day ICE from Swiss/Basel to AMS-try to avoid that! Go for a direct ICE from FRA/HBF if it can fit into your plans. But even then it may mean you have to change from domestic ICE to the few international ones still able to run-like in Kóln.
TS was planning to use ICE 120, which does originate from Frankfurt Hbf. Quite usual that the "verkehrstage" are shown separately for different sections.