Linking Sharepoint lists items across lists and 'Looking Up' columns

So you have multiple columns that exist as separate data values in multiple lists. Let's say we actually build this connection for Item 12345 that pulls in data from the other 2 lists based on the Flow copying the value "12345" to each of your lists. What happens when Item 12345 is accidentally edited to Item 1345?

Now lets do math. How many fields is Flow copying? Multiply by 3 lists? Multiply again by the number of list items and that is the number of potential data mismatches you have. The multiple list method may protect one or two fields from accidental or malicious changes, but only by putting your entire dataset is at risk.

In my experience, the "requirement" to restrict access to certain fields really masks a concern that some person who doesn't know what they're doing might accidentally change a value that breaks the process, such as assigning the wrong SME to a task. Do the 6-Sigma Why thing. Why do you need this requirement? Why do you have that concern? Why is it a problem if someone accidentally edits the wrong field? By doing that, I can usually get to the root cause/driver, such as "if the wrong SME is assigned, service delivery is delayed while we fix the assignment and X bad thing happens". 

Now, that I've identified the actual need, I can usually find ways to address the concerns satisfactorily, such as "let's create a defined list of SMEs for each service so a user CAN'T pick the wrong one". The important thing is to help people understand how separate permissions on separate lists will actually make their problem worse. After all, they wouldn't have this "requirement" if they weren't concerned about dirty data in the first place. 

Once we get past the separate lists, then there are things we can do that to guide users in the right direction and minimize their access to fields they shouldn't mess with. We can use views on pages to decide what fields they see. Carefully distributing fields across forms helps determine what fields they can access. Depending on the edits they need to make, quick edit can be a good option. 

But the thing that will convince people they're data will be safe even if everyone can access all the fields is line item version control. Seriously, this will make you a ROCK STAR. Process owners will be able to see who made exactly what changes to which fields on which dates. And if a mistake was made, they can restore an earlier version of the item just like with documents. No harm, no foul. :-)

However, if multiple lists is an inflexible requirement and you risk getting fired for challenging it, then you're stuck with multiple lists and I would focus on lookups rather than copying data fields. At least then the data integrity is preserved.