Child dependant MORE additional docs requested

I posted previously about how additional documents were requested to prove sole responsibility of my child. They gave us 5 days to submit those documents, which we did, and now they have sent the same request again, this time giving us only 2 working days. Does this mean that the additional documents we gave them weren't sufficient? And are they looking for something specific that I haven't already provided. (For example, do I need more evidence to corroborate what I already gave them?)

For context, childs father has not been involved, no custody order because paternity was not established

This is everything we gave them originally:

1. Childs passport (which i had to prove i did not need consent from another parent to recieve
2. Child's birth certificate listing me as the only parent
3. Recent permission slips for school
4. Multiple emails for each year my child was in school, of communication between me and childs teachers, counselors, after-school programs, and out patient therapy. A few of which refer to parent teacher meetings I attended, or ask for my permission to talk to doctors with releases attached
5. Release form for emergency services for my child, signed by me

All the additional documents we sent for the first request:

1. Notes from the past 3 doctor appointment saying I was present.

2. The contact sheet from each school my child attended, listing me as the only parental contact (they said this is the most they can provide me with. I asked teachers and school counselors and EVERY school told me they can't write letters. Even talked to principals. One school said the reason is "we have to stay out of stuff like this" All I asked for was a statement that I was the only parent they communicated with/met with)

3. About 15 more emails of communication between me and past providers throughout the years

4. Tax returns from the past 5 years listing my child as a dependant who has lived with me for 12 months each year, and confirmation emails that these were accepted

5. Two photos from every year of my childs of life of me there with them

6. Notarized affidavit from myself confirming that i have sole custody, and am solely responsible

7. Notarized affidavitS from childs maternal grandparents, confirming that the father has not been involved

8. my passport bio page and signature so I can be identified in the photos

9. Official letters from his past two doctors stating that I was the only parent present at appointments

10. Another permission slip I missed the first time

11. An emergency room health visit summary that mentions me and gives instructions specifically for me about the care of my child

12. Travel documents (train tickets with my child's name on it, and flight tickets from a visit to the UK)

13. A letter from myself, explaining our situation and how I have been solely responsible

Could it be that they are looking for something to fill a specific gap in information? Unfortunately I do not have documents from my childs early years. Also, his most recent doctor was unable to give a statement because they are no longer with the clinic, and I was told it could take awhile to track him down for a statement.