You can see if your address is potentially a two stage installation by putting your address in here
https://www.broadbandchecker.btwholesale.com/#/ADSL/AddressHome
if it’s KCI2 , then at survey it was expected that the preparatory work to get the box on the wall and the cable /duct to it and the actual internal work inside the house needed to be done separately, this is often when there are clear issues to overcome, if ( for example ) excavation from the footpath to your house wall was needed , that’s done separately to the internal work as unexpected delays may occur on the first stage , so generally only when the first stage is completed satisfactorily, a ‘proper’ installation appointment made with the customer to ensure internal access is available on that date ….the first stage doesn’t need anyone to enter the property , and shouldn’t be contractual so delays don’t start any sort of compensation clock , it’s no issue if the customer is upgrading from copper pair service as that remains untouched.
If your address shows single stage , unsurprisingly it’s envisaged that everything needed inside and outside can be done on a single visit, like the property is already ducted (so modern housing mid 1990’s onward) or a straightforward overhead installation from a pole
TBH , Openreach are more likely to be correct as they are doing the work
