When you find a letter after the number, such as BX2763 and then BX2763A the A designates that there was a modification to the initially released part BX2763, it doesn't indicate that a hydraulic cylinder has been added. I have never seen where a completely different mounting system resulted in the addition of just the letter. I have seen when people mistakenly replace one decal with another thinking that it didn't matter if it had a letter after the number. This frequently happens with snowblowers where a case is changed and the original snowblower number is replaced with the wrong suffix letter, causing many problems when researching repair parts.
In the above picture, Ken Erickson mentions a serial number break, which means that some part used on the original blade is replaced with a newer part and the newer part will also have a new part number. Sometimes you will need to search both part numbers to see exactly what the part change is. Sometimes the new part will be backward compatible, and that will be indicated by showing the original part number being discontinued, and the new part number will supersede the old part number.