There's no easy way out of this. You'll have to review all of your existing automation and set up criteria accordingly.
In all of them make sure that RecordTypeId is not null. That's the first step. And then, might have a couple of options on how to approach this. I'm thinking that, if you long-term plan is to consolidate everything into a single instance, you will review all of that automation at some point:
Approach 1: Update existing records or new records
This will require you to review all of your automation. You might want to create a field to identify records of specific records types, like a Boolean or picklist field. And then you add that to the criteria of your automation in all Processes, Apex, Flows and Validation Rules you have.
Approach 2: Evaluate records as they are processed
This involves reviewing all of your automation as well. And is similar to the #1, but you'll have much more work because you'll be checking for the record type in each and every automation piece you have.
For Validation Rules especially this might be a challenge because you'll be checking the RecordType.DeveloperName for 50 different values.
To be honest, I'm with the opinion that you should review your org structure with your stakeholders and reduce the amount of record types you have on your object. Personally, I can't envision a scenario where 70 record types are necessary on an object. If we are talking about different layouts for those, remember that in the Lightning Experience's App Builder you can conditionally display sections and fields according to more flexible criteria (including formula fields), so that might be an alternative for you to build your layouts, if this is the case.
