Hi,
For 1) and 2). Our GIS calculation is now entirely based on our implementation of the Old Age Security Act. The act describes how to compute the amounts for OAS, GIS , Alllowance, and Allowance for survivor, and that's how we do it. We do need to also use the updated maximum amounts that are indexed every quarter (from https://open.canada.ca/data/en/dataset/ff1e4882-685c-4518-b741-c3cf9bb74c3e). We don't use the government pre-computed GIS tables (which apply only with full OAS pension, and we can reproduce in that case), and we don't make approximations for the clawback. I've clarified the eBook section on OAS/GIS.
With our calculations, indeed the GIS amount and the income threshold is increased for pensioners with partial OAS pensions, the retirehappy blog is entirely correct. The second blogger is also correct in their analysis of the tables, but if they want to derive the calculation, they should read the OAS Act :)
The OAS and GIS/Allowance calculations are made in each year of the TIME MACHINE so they adapt to circumstances and income levels in each year.
3) Yes we implement the QPP supplement, we refer to it as the PRB (Post-Retirement Benefit) for both QPP and CPP (although they are calculated slightly differently).
BTW If your parents are 65 or over and the TIME MACHINE calculates a GIS amount in all years, these runs will not count towards their MoneyReady App free trial.