Does an employer have to state that the collective labor agreement has expired?

Questioner

I worked for the employer for 23 years and had to stop for medical reasons. Now a back payment must be made for outstanding ADV and vacation days from the last 5 years. The employer now claims that the collective labor agreement that was concluded at the time is no longer valid and that he therefore no longer has to do anything. I now have to prove that the collective labor agreement is indeed still applicable. Isn't it actually the employer's job to inform me of this? Shouldn't a new collective labor agreement or AOK have been drawn up then? The funny thing is that last year I asked him under which collective labor agreement we fall and I got the answer: Electrotechnical Retail and even sent me the collective labor agreement by email??

Lawyer

There are various ways in which a collective labour agreement can apply. One example is via a generally binding declaration. The minister has then determined that a collective labour agreement applies to employers and employees who, in short, meet the definition provisions as included in that collective labour agreement. If rights have been built up during the validity period of the generally binding declaration, they will generally not expire later when the validity period of the generally binding declaration has expired (unless those claims have expired).

Questioner

So if I understand correctly, the burden of proof is not on me? I can assume that the CAO was still the same as it was at the time and that my employer should have informed me by means of a new CAO or AOK?