All changes done in the source need to be marked. Marking makes it possible to trace changes and to collect all parts of a solution and provide it to the customer.
Mark with the solution number
A solution could cover several sources. When a solution turns out to be a bad fix all adjustments of the solution need to be found. To be able to do that, all changed need to be marked with the solution number.
The solution number makes it possible to discuss the error with the Customer and the Support Analyst. You are sure you are all talking about the same problem and thus about same source(s).
Solutions that turned out to be Bad fixes must get an indication so Customers are aware of it. When a new solution fixes the bad fix, a reference to the new solution must be given on the old solution so customer can download it. All this must be visible for Customers when they look at solutions in their self-service solution database.