Estimated time is hugely inaccurate anyway.
Biometrics reuse happening later is totally OK.
When I had I-751 pending, my biometrics were reused after about 5 months after filing. However, I've seen many cases stuck in initial received state. Those cases got biometrics reused after 11-12 months and decided before my case and other similar cases with biometrics reused earlier.
You cannot read too much into this.