We have built a .NET app that uses our Enterprise WSDL to pull data from Salesforce , and we use a dedicated development sandbox for ongoing development.
Previously, looking at the WSDLs generated from the two orgs, in addition to the SOAP endpoints starting w/ login.salesforce.com vs. test.salesforce.com, the Id at the end, following the API version number, also used to be different between the two. I don't know what that Id refers to - it's not the Org Id, or I wouldn't be asking the question ... probably.
I just refreshed that dev sandbox and generated new WSDLs (Production/refreshed sandbox) and the endpoints are identical. Aside from the 'test' vs. 'login', does that last ID being the same matter anymore? (That dev team doesn't like to 'just try stuff out' w/o evidence -- engineers...)