Tracking changes in stored procedures within a database
Don't be tempted to re-invent the wheel. This problem has been solved many times before you came across it.

Take a look at schema comparison tools, such as those available in SQL Server Data Tools (SSDT), and commercial options like Red-Gate SQL Compare.

Going forward you can also use DDL Triggers to log certain DDL events, helping you catch outlying changes that only happened in one place. If you want to do more reading, I have a few tips about this handy feature here, here and here.