Malcolm Needs's post in Tube method vs Column Agglutination Technology for Grouping was marked as the answer
Column Agglutination Technology (CAT) is superb at detecting IgG antibodies, and also at detecting certain "cold-reacting" antibodies (such as anti-I and (because of the pH of the column) anti-M, BUT the manufacturers themselves state quite freely, that they are not designed to detect all ABO mis-matches, because most ABO antibodies are IgM (anti-M are usually a mixture of IgM and IgG, but also react preferentially at a low pH).
Malcolm Needs's post in Can I get your opinion or insight on this? Thank you. was marked as the answer
In terms of the function of the various ABO blood types, there have been a huge number of peer-reviewed papers written on the subject (and the number has exploded with the advent of COVID19). I would seriously defy anyone to keep up with all of these, but I would recommend reading pages 42-43 of Reid ME, Lomas-Francis C, Olsson ML. The Blood Group Antigen FactsBook. 3rd edition, 2012. Academic Press. ISBN: 978-0-12-415849-8.
In terms of how they evolved, it is so far back now that it is anyone's guess, but slides 28 to 32 of the attached lecture may give you some idea.
In Depth Lecture on The ABO and H Blood Group Systems.pptx
Malcolm Needs's post in Does anyone knows what does “+s” mean? was marked as the answer
It simply means that the P1 antigen is particularly strongly expressed on these red cell samples. Therefore, if you come across a weak anti-P1, it may apparently react with these particular red cell samples, whilst apparently not with, for example, the third red cell sample shown in your antigram. Although not identical to dosage, per se, it is fairly synonymous with dosage at a phenotypical level.
The strength of the expression of the P1 antigen is an inherited trait.