Edit "Member Since" Date

Is there a way to edit the "Member Since" Date for Member Areas? Or even change the label to read "Member Since"? My organization just recently switched to Squarespace and added Member Areas as a way to provide a portal for our organization's members. However, when members view their accounts, they are shown a "Member Since" date, with the date being the date they set up their membership account on the new website. Yet, we have members who have belonged to the organization since 2014. It seems strange that we wouldn't be able to update their join date on their profile or, at the very least, edit the label to read differently.

I've tried using custom code (both CSS and Javascript) to edit the label, but because it is coded in an iframe, I can't override the label. Any other ideas?