Good Morning Everyone

I'd like to take a second to show you what I'm finding when trying to sort this collection(s)...
Below is the original envelope containing some stamps....It says....

However, it contains the following three stamps....

Here are the backs....

Each one front and back........






First, is it just me or are these vermillion? Can't possibly be SC 146???
Bear in mind a couple of things....I know for certain there are at least three separate collections in the hoard....One collector was super serious and organized and had a great many of the stamps properly identified (although they are newer (1940s-1970s)....The other collector wasn't as organized and had so many of the stamps incorrectly identified....although neatly as in this example...and almost all of this cache is pre-1940.
So, now I'm having trouble understanding how to properly identify the SC 100s-200s, I've been to several sites, but I'm getting really confused on the paper type and secret mark stuff.
I have a bunch to go through

Is there a preferred site that explains it really well?
Like I can see the third stamp in this set pic is obviously different, and I think if I understood better it would jump out as SC#X....as I'm sure it did to you!
Thank you so much for your help!
Another example is a tiny glassline I found with 2 stamps and a note saying could these be the 596? I have looked at them briefly, and think in no way shape or form they could be,(and 2? really...) But I'm thinking the last time this section of the hoard was touched was approximately 1964-65. So, who knows what's in here....I'm going with if there are so many stamps, and the collector was serious (albeit limited on identification materials or knowledge)...There really could be a rare stamp hiding in these masses of envelopes! Only t-i-m-e (thank you Hal

) will tell!
Take Care Everyone and Have a Blessed and Wonderful Monday!