First UK passport application at Post Office

Hello,

I used the Post Office service to apply for my first UK passport on the same day of my naturalisation.
They collected my Italian passport and naturalisation certificate as part of the application, saying they'll be sent the next day with Special Delivery. However, they did not give me a tracking number, they only gave me a passport application tracking number claiming that would be enough.

It was naive of me to not insist.

After 7 days, the status of my passport application still says "send your documents" and after speaking with the passport office, they told me that normally supporting dos are scanned 48h after reception, and they are unable to retrieve my documents without a delivery tracking number.

For anyone who used this service, how long did it take for your supporting documents reception to be acknowledged in your passport application progress page? After how many days should I start worrying they were lost?

Can you ask the post office who sent your envelope if they have anything on their records? Do you have a receipt of the envelope being sent?