In my years of experience as a Pilgrim Office volunteer, I have seen the entire range of stamping.
There are pilgrims who combine multiple credencials to hold all their sellos. These folks collect the sellos, pretty much the same way others take photographs with their smartphones.
When they arrive at the counter at the Pilgrim Office, their credencials resemble huge origami paper sculptures. If staff are lucky, the pilgrim has already arranged the credencials in chronological order. If not, staff must do this.
Then, on the other end of the spectrum, there are folks who cannot seem to understand that you need enough sellos, throughout a Camino, to establish progress along a route - point to point - as well as the chronology involved.
They also did not read the credencial itself, or pay attention here in the forum, to understand that once you hit the 100 km threshold on any route (200 km if on a bicycle), TWO SELLOS are needed per day. It is really a very easy thing. Yes, I know it is in Spanish. But, that is what online translators are for.
When there are excessive sellos, staff and volunteers have to parse them to create a chronological narrative to support a pilgrims claims of having walked "X" route in "Y" days. This, of course, takes time.
Now that the Pilgrim Office arrival process relies almost exclusively on online pre-arrival registration of your personal data, significant time is saved at the counter.
This semi automated process works much in the same way that the new EU ETIAS visa free pre-arrival online process will work, and how the existing US ESTA process works for many non-US nationals traveling to the US. In all three contexts, you submit your personal information online, in advance of your arrival.
For the national border systems, you receive an admission code from the appropriate border authorities. In the pilgrim context, you receive a QR code to announce your arrival at Santiago to Pilgrim Office Security.
When Pilgrim Office security scans this QR code, you receive a queue order number. This also sends your data to the laser printer queue, so your Compostela and Distance Certificates (if requested) can be printed in a beautiful script font. When you arrive at the counter, your certificate(s) can be rapidly printed and delivered.
Then again, if a Compostela is not your goal, then it does not matter what you do. The issue here is that, if you change you mind, from NOT wanting a Compostela to wanting one, but you only have few and infrequent sellos in your credencial, staff have to look elsewhere to try to substantiate your claim to having walked a specific Camino to qualify - if possible. This is yet another, indirect reason, why using a smartphone on your Camino is a good thing.
In this case, the most common thing staff will do is to examine the meta data for your photographs to determine where the photo was taken and on what date. I have seen eligibility for MANY Compostelas "saved" this way. But, it takes an inordinate amount of time and patience.
So, just in case you MIGHT want a Compostela, please just get the sellos - one per day beyond 100 km if walking (200 km if by bicycle) - then TWO per day once you hit the 100 / 200 km threshold: Tui. Ourense, Vigo, Sarria, Ferrol, etc. by foot. Figure out the 200 km threshold if by bike.
Bottom line - if in doubt - just get the extra sellos.
I hope this helps.
Tom