National Insurance Contributions for time spent overseas

I recently found out about the option to pay NICs for the years going back to 2006. I've spent quite a bit of my life living and working abroad including 3 years in Canada and 7 years in Germany. I understand (from https://www.gov.uk/new-state-pension/living-and-working-overseas) that my years in Canada could be taken into account when claiming my pension (which won't be for another ~30 years). Is there a way to get confirmation of that so that I have a clearer idea of whether I should be paying voluntary contributions? I also understand that my years in Germany, can count towards the 10 years to be eligible to receive the pension, but won't impact the value of the pension. I understand that if I want to pay voluntary contributions for these years, they might then come under class 2 rather than class 3. However I see from https://www.gov.uk/government/publications/social-security-abroad-ni38/guidance-on-social-security-abroad-ni38#paying-voluntary-national-insurance-contributions-while-youre-abroad that has to have been employed or self-employed prior to moving abroad. I presume that since I was on a PhD stipend prior to moving abroad, that I can't take advantage of this and would have to pay class 3 NICs, yes? P.S. I have tried to call the Future Pension Service about this but always get disconnected after getting through the various options.

Hi,
Before deciding to pay voluntary National Insurance contributions, we would advise to apply for a State Pension forecast. The forecast will detail your current and future entitlement to a UK State Pension:
Check your State Pension forecast
The DWP Future Pension Centre will be able to help you regarding your periods in other countries. Their contact details may be found here:  
Contact the Future Pension Centre
When you are ready to pay voluntary National Insurance contributions whilst overseas then please complete the CF83 application form and then our International Teams will be able to assess whether you may pay voluntary class 2 contributions.
Thank you.
 

Hi, I did eventually manage to get through to the Future Pension Service, but all they told me was to complete the CF83 application form. When I eventually heard back from that, the information I received was exactly the same as in the State Pension Forecast, with no indication of how my time abroad impacts my NICs, so I find myself in the same position I was 2 months ago. Given how I'm running out of time to make a decision on this, I was thinking that I should at least pay for a couple of years just in case. However, even that process does not seem easy. A bank transfer seems like the best way to do this, but the information on what to put as my reference is unclear and there's no information on how to make it clear which tax years I'm paying for. This process definitely needs a lot of improvement.

Hi,
If you could complete our form CF83 then we will be able to provide you with details of any voluntary National Insurance contributions that you may wish to make.  
As long as we receive your CF83 application form before 5 April 2025 then you will be given extra time to make any payments that you may wish.
If you have already completed the CF83 and wish to make a payment of voluntary contributions then details of how to make these are available via:  Pay voluntary Class 3 National Insurance