just wondering, for those firms report interest in operating cash flow, do you add back after tax interest regardless?

Yes, When the interest is deducted in the calculation of CFO (which is the case under US GAAP), you have to add back the after tax interest expense. Under IFRS interest expense may be deducted either in the operating section or the financing section. If deducted in the financing section you do not need to add it back.

^good job.