Peter, you MIGHT be able to get the necessary details you need by pouring through the Electrical sub’s documentation/invoices, then again you MIGHT not. Let’s start with the MIGHT not, based on my experience, one of the more difficult feats to pull off is getting enough of the client’s attention to get them to fulfill document requests. I have waited 6 months for information from clients only to find that it was still incomplete. Put that aside, even if you did recover all of the documentation, depending on the complexity of the project, you’ll need to turn yourself into the subcontractor’s bookkeeper for hours on end (if not more), creating a spreadsheet to document each and every “subcost” until you’re finally able to recreate the trade completely. That is unless an invoice is missing or is too difficult to read or any one of many other possibilities. And, if you complete that and are reconciled to the cost’s total, that trade is done but now you have to rinse and repeat on Plumbing and any other trade you are rebuilding. I don’t know how you value your time but l I value mine very highly, as should most Cost Seg engineers and because of that, the above process (which is by no means guaranteed to bare fruit), is not a good use of my time. I’d rather go immediately to something that will work every single time. That’s why we rebuild each trade one component at a time based on the particulars of the project given. This is a painstaking process but at least you’re not jumping down rabbit holes you’re not sure you can get out of. Also, I have a secret weapon. SegStream rebuilds each trade component by component (using models built by our team of architects and engineers) for me just by answering straight-forward questions about the property. For the purposes of a Cost Segregation, the recreations from SegStream are as irrefutable as the post hoc bookkeeping you might do on a mountain of subcontractor invoices that will take you much longer to complete and are not guaranteed to work every time.