I’ve never heard of this before, can you give a reference?
This is all I could find in English (but you will notice your 1962 liturgical calendar has no fish or partial fish symbol for Wednesday, as it does for Friday and Saturday, because this year it falls on the Feast of St. Matthew):
"A second indication of this new reckoning is provided in the Proprium Sanctorum section of the 1962 Missale Romanum, wherein a rubrical note is printed after the collects for the Feast of St. Matthew, Apostle and Evangelist (September 21):
Et, in Quatuor Temporibus, fit commemoratio feriæ.
Here, the term feriæ is referring to the Ember Day which is a II class ferial. This note indicates that the September Ember Days might be observed within that time frame—though they could also be observed between September 18 and 27 as the earliest and latest dates."
https://www.romanitaspress.com/reckoning-sept-ember-days En France, here is the FSSPX online Ordo (which reduced Ember Wednesday to a commemoration, and the liturgical color red for St. Matthew, whereas Friday and Saturday are Ember Days, purple, and fast/abstinence):
https://laportelatine.org/ordo