Stolen iphone and forgotten apple

Hi,

A few days ago my iphone got stolen.

I tried to locate it using a friend device and declare device stolen, but in order to that - I had to sign in with AppleID password - which iforgot - so I could not declare my phone as stolen/lost & delete data.

After a few failed attempts I got a message from apple that now the account is a recovery period, and I have to wait a few days until i could retry to recover my password and restore all the data from Icloud.

Now, with a new Iphone, I cannot login to my original AppleID and have to wait for the recovery period to end (20.6).

Questions:

1) I did not declare phone is stolen via "FindMyIphone" - can the thief do a DFU mode and sign in into a new appleID account ?

2) If 1) is "yes", does that mean that I will not be able to declare a stolen device & delete all of its data, once I will retrieve the password, because now the device is in use of other apple ID ?