I made another earlier promise to look at how and if other people's mymaps files persist when using Google Maps. This was going to be difficult but now that @David Tallan has produced this combined mymaps file it has become much easier for me, thanks again DavidSo. I took @Doughnut NZ KML file and added it to a Google Map. Then I added in the Portuguese Caminos from the Dutch site to the same map. Then I downloaded the "too big" KML file from the Dutch site and removed the Caminos @Doughnut NZ had kept and added the remainder to my Google Map. That left me with a Google Map with many of the routes in Iberia. Then I went digging through my forum bookmarks for favourite albergue/favourite restaurant/favourite bar resources and recommendations and added those places to the map as well.
What I ended up with is here: https://www.google.com/maps/d/edit?mid=1vf4iNGwIJhcsChA-pLk5uanLVshEB806&usp=sharing
If you have a place you'd like added to the map, let me know.
Once I have created the new routes in mymaps I prefer to use them from within Google Maps because G Maps is so much more powerful for searching and for it's other features.
I can access my own mymaps files from within G Maps but I wasn't sure if that also applied to other people's mymaps files like the one created by David. It looks like I need not have worried. Provided that you have opened David's file at least once within your own copy of mymaps (by clicking on his link) then his files remain within G Maps.
On an Android phone running G Maps, start the Maps application and touch Saved down the bottom of the screen.
Then scroll right down to the bottom and touch the Maps link
Then scroll until you find David's map and touch it.
In this particular case, David's map is at the top and so it is easy to find but it looks like every new map that you create with mymaps is put at the top and pushes everything else down and so it may not stay at the top.
Fortunately, David has given it a good, meaningful name and so it should always be easy to find even if it is not at the top!