Thanks to all for the help with this. Only for info - I completed the CF83 and sent in October 2023. I got confirmation of class 2 for the missing years in May. I made a full payment at the end of May and followed up today as it is not yet shown as allocated. According to the advisor (very pleasant) - the current backlog for EU payments to be allocated is 45 weeks! She did acknowledge receipt of my payment and said that once I had paid, the deadline no longer applied. We will see ....