Using old losses not included in recent loss carried forward figures

I will need to pay CGT for the first time this year. I know I have some losses from between 2000 and 2013 that I declared at the time and have never used, and would like to use these now. I have this year systematically recalculated my capital gains for all previous years using my records, and in that way can identify which years had losses carried forward, and how much they were. But I no longer have copies of my returns for those years with which to verify that what I've calculated now exactly matches what was declared at the time. I have tried to get this data from HMRC, but have so far been unsuccessful. Also, because I had until now lost track of these losses, they were not included in the cumulative loss carried forward figure in my returns of recent years. Is the best solution to submit my return for this year, claiming all the losses I believe I should be able to use to offset my gains, with a detailed breakdown of the amounts and years of amounts carried forward? I would also categorise the recalculated amounts as estimates, so HMRC can check these against their records.

Hi Christopher King,
If you telephone 0300 200 3310 or contact us on webchat, HMRC will be able to check these old returns to confirm any losses declared.
Thank you.

Thanks. I was able to get the answers I needed from a human advisor via web chat. There's was nothing to indicate speaking to a human was possible, when the bot either declined to help or gave unhelpful answers, but asking to speak to a human worked.