As Herts and Bucks have no track record of delivery it is difficult to say.
However looking at other areas where there is a delivery record, Wales for instance, they have delivered a substantial number of new exchanges since they started last June. See the area from around Anglesey
down the coast towards Aberystwyth as an example.
They appear to be doing all the Cabinets straiight away ( Except where there are particular problems), leaving the EO ( Served direct from the exchange) customers until later. Following the more customers per £ principle.
The Wales map is based around exchange areas so is clearer in one way but doesn't show the detail that the Herts map so is harder to pinpoint premises. Most of Wales didn't have superfast so infill wasn't an issue!