Knowing that it should be BITTLES , then I can easily see that in the entry, but without that prior knowledge I could have been in difficulties ..............
Given the degree to which the interpretation is open to argument (i.e. without prior knowledge) you may well find the the GROS stance is that the index entry should stand as it is.
Personally I'd argue for the approach where the BETTLEY entries are allowed to stand but BITTLES entries are added to the index. If I remember correctly Ancestry adopt a similar approach.
David