What does the Price for Work Done to Date mean under NEC4 Options A and B?

The Price for Work Done to Date is what the Contractor is paid for the work itself, and under the priced options its definition in clause 11.2 ties payment to the pricing document rather than to cost. Under Option A it is the total of the Prices for each group of completed activities and each completed activity not in a group. An activity is completed only when it is without Defects which would either delay or be covered by immediately following work, and there is no payment for an activity that is partly done, however nearly. That makes the activity schedule the cash flow document: large activities mean long gaps between payments, and an activity with a Defect in it is not paid at all until the Defect is corrected. Under Option B it is the quantity of work completed for each item in the Bill of Quantities multiplied by the rate for that item, plus a proportion of each lump sum which is the proportion of the work covered by the item that has been completed. Option B is remeasured, so the quantity paid is the quantity done, not the quantity billed. Under neither option are Plant and Materials delivered but not incorporated part of the Price for Work Done to Date unless the activity schedule or the bill provides for them, which surprises Contractors used to other forms. Implemented compensation events change the Prices, through the activity schedule under Option A and the bill under Option B, so an event that is not implemented does not reach the payment. What goes wrong: Option A applications that claim percentages of activities, or activities complete in the Contractor's view but carrying Defects; an activity schedule never updated for compensation events; Option B applications measured against bill quantities rather than site measurement; and lump sum proportions asserted without any basis.