It depends. As others have said, each "lot" was only created upon first being sold rather than by the map, so if that is the only consideration, you would survey as if each lot were created and surveyed at different times.
If the deeds have referred to particular lots in the plat, and/or incluude a metes & bounds description which follows the lot dimensions, and you have evidence that the entire unrecorded subdivision was surveyed together, then you are retracing a survey that laid out all lots together and all evidence of that survey, regardless of where within the survey and order of first conveyances of the lots, would have equal weight.
Whether or not the distance and direction calls in the individual deeds would be treated as calls in simultaneous or as calls in sequential conveyances will depend on how your state courts have treated similar situations. In New York, they are treated as sequential even with the plat available and evidence of a survey of the entire subdivision. You would not apportion excess or deficiency between found monuments where intervening monuments are lost, but hold record distances according to junior/senior relationships of the first conveyances. In California, if you have the plat and any evidence of a survey performed to create it, you would treat the parcels as simultaneously created by the survey that the plat reflects.
Your question is one that may change depending upon several different other details and upon jurisdiction, but I think that most jurisdictions would tend to be closer to the California view than to the New York view if the deeds refer to the plat and a verifiable copy of the plat were available.