conditional formatting an overriden formula cell

i would like to create conditional formatting that highlights if a cell is overridden. i am aware of the isformula idea which is great if someone hardcodes a formula cell, but i would also like it to identify if someone adds a suffix to a formula ["=sum(b6:d6)+5"] where the "+5" was tacked on to "override" the formula. in this case the isformula idea fails. any ideas on how to circumvent this?
in the attached example, a6 should be highlighted in addition to a8.
The formula will change with the row reference (now shown in this example) so the formula isnt static in the sense of the row reference but the formula is always the same outside of this (always summing B to D but just on different rows).
i have tried the solution proposed beginning on row 12 but i am not sure how to set it so it considers the formula on row 13 for all subsequent rows (i doubt i have the formula correct).