1. I think that's a myth. "Correction" should be done at any albumin value. A high albumin will obviously elevate the total calcium just as a low albumin does the opposite. Exactly one study had findings that suggested one should not correct total calcium for high albumin, but its findings were never replicated.
2. A bigger problem is that albumin-corrected calcium has been repeatedly shown to be poor at deducing ionized calcium status at any albumin value. Here is a link to a much better--and externally validated--method for deducing ionized calcium status:
qxmd.com/calculate/calculator_704/predicting-ionized-hypocalcemia-in-critical-care