Kametz Katan in Azhkenaz

Although the average person will tell you, and some scholars too, that the Azhkenazim did not have a Kametz Katan, a review of old Selichos, Siddurim, and Machzorim will prove otherwise.

Here is a little background: The Kametz Katan and the Chataf-Kametz are pronounced the same way. The Chataf-Kametz follows the rules of a shva, and the Kametz Katan is the short vowel for the Cholem. Radak explains that the nikkud is the same for the two of them: The chataf kametz has the shva and the Kametz under a single letter, and the kametz katan has the shva under the next letter. Radak does not mean that they have the same ruleset, but that they are pronounced similarly and have the same nikkud.
A review of old Azhkenazi Selichos, Siddurim and Machzorim will show that a kametz is marked like our kametz is marked today. A kametz katan, however, is written as a chataf-kametz. This is not mistaken for a chatef kametz because the next letter has a shva under it. So you know that the kametz is katan and not chataf-kametz.
Have a look at the JNUL Digitized Repository Liturgy section and take a look at the Selichos Minhag Azhkenaz, printed 1475. You will see קדשו,אזנך etc. - words that have a kametz katan written with a chataf kametz. under the kuf and alef and a shva under the dalet and zayin. Take a look at the other Siddurim, Machzorim, and Selichos, at least till the early part of the 17th century and you will find the same.
The image to your right is from Machzor Augsburg printed in 1536. Note the words ישרם and כפרם in the section אז מאז זמות. They are words that have a kametz katan and they are written with a chataf kametz.
As you move later and later you will find fewer words noted as kametz Katan, although the word קדשו appears to be marked with a chataf. What changed? Do we know of any discussion, responsa, decision abolishing the Kametz Katan? Or is it logical that less and less people knew (and cared) to pronounce the kametz katan correctly?
I am not done with this topic.