For what it’s worth, þ and ð can sometimes be used interchangeably for English, particularly now that the lines have been blurred with the consolidation into “th” (e.g. ‘with’ is usually a soft ‘th’ for me but ‘without’ is hard; ‘cloth’ is soft but ‘clothing’ and ‘clothes’ are hard, etc.), and English overall went through a substantial phonetic shift between when those letters were used and today.

But if OP wants to be pedantic about archaic letter use, I withhold the right to be equally so.