It sounds like I may need to find a different place to get the first stamp?
When I first walked the Caminho from Lisbon, which was in 2007, there was no mention of the Igreja de Santiago anywhere or by any group. The cathedral was the starting point. The first arrow was (and still is, I think) down low in the cathedral wall to the right as you face the cathedral. At that time, the credential was only available at the Igreja dos Martires (in Chiado) and in one other church I can’t remember. And I don’t think the cathedral even had a stamp. This is all a modern fabrication, not a bad thing, but nothing that should make or break a caminho.
The cynic in me says that the church realized they could raise their profile and have tried to make a statement about being the starting point. But as far as I have been able to see, though there may be an arrow in front of the church itself, there is nothing that marks the route from the church to the caminho, so anyone who goes to the church just heads down to the cathedral to start.
I understand the attraction that starting in the Church of Santiago might have for people walking to Santiago. Seems like a nice bit of synchronicity. The same thing happens on the Camino de Madrid — people go to the Iglesia de Santiago in old Madrid for their first stamp (and credential, I think), but from there to the first arrow is about 8 km of unmarked route through the city of Madrid. It’s a nice touch, but I don’t think there’s any historical claim about the “true“ starting point either in Madrid or Lisbon.
I don’t think anyone should be too upset about starting their caminho at the Cathedral, where you can get a stamp and a credential. It’s only a few hundred meters from the Santiago church, though, so nothing wrong with going a bit uphill, seeing the front of the church, and then turning around and going back down to the cathedral.
I have a memory that one time in the distant past @amsimoes
took a group of us to the Santiago church and it was open. I was in Lisbon for work, I wasn’t walking, so I didn’t even ask about stamps. But I think that is the only time, of about 15 or so strolls by, that I have seen the church open.