As a break from a place more-French-than-France, I'll return to the place more-French-fries-than-France.
I'm assuming you have got all of the routes right, and OSM has road numbers where there shouldn't be (eg N617 in central Liege).
N1 (Antwerpen):
- N11 point merged with A1 exit 5 point (one point per interchange)?
- between N129 and R10 route doesn't currently exist: split
N1 (Vilvoorde):
- N1a_Sta -> N1a
- add a point or two in Buda for indirect access to R0?
N1a, N1b: both fine
N1c
- HofEik -> HofEikLaan
N2 (Zaventem):
- AveComGem -> AveCom or GemLaan
- R23_W -> R23
N2 (Diest):
- R23_E -> R23
- merge N29 and A2(24)? ditto N739 and A13?
- R26_W -> N10/R26?
- R71_W -> R71
- R70_W -> R70
you've chopped up routes, but continued to treat them as one big route. Either put them back together, or drop superfluous directional disambiguation.
N2 (Bilzen):
- R70_E -> R70
- R71_E -> R71
N2c: fine
N2d:
- VanLaan -> DokVanLaan
N3 (Tervuren):
- is KorLaan the right label (this area by the is a mess!)?
- is KerStr the right label?
- R23_W -> R23
N3 (Liege):
- R23_E -> R23
- N671 off (and as theres no direct connection between two routes, is it the right place?)
- N90 and RueJup off
N3e and N3i fine
N3g:
- called N603 on OSM
- GSJ in the middle there?
N4:
- point for Rue du Trone?
- MaaLaan -> AveMae (Brussels is de facto Francophonic, even if de jure bilingual)
- EurPirLaan -> AveEurPir (ditto)
- TerWeg -> ChaTer (ditto)
- Avi -> RueTom
- Flg -> CheRen? Fla?
- Fls -> RouStr
- Man -> RueMan
- RueAss -> RueWac
- RueDec -> Rue26Dec
- RueBas -> RouBas_N? RouBas_S
- BEL/LUX_Mar -> N23 (doesn't matter that it's the Luxembourgish one and the N4 is the border)
- BEL/LUX_Arl -> BEL/LUX