PCM sticker says authorized software update

The computer is somewhat generic and will work in multiple models until the software specific to your vehicle is installed. After that, there can be software updates to address newly-discovered emissions issues, customer satisfaction improvements, or other functionality changes to improve performance or reliability. The original sticker has the part number assigned to the computer / software package for your model. That means if you should find the exact same part number in a salvage yard, that computer will run your engine.

When new software is installed, similar to updating the operating system on your home computer, that computer could get an entirely new part number. This is why we often have to go by model / engine size / year application when looking for a used computer rather that relying on the part number.

In other cases, when minor changes are made in any part, including computers, only the last one or two letters in the part number will change. For example, a common radio model I work on is "4704383", but the number on the sticker might be "4704383AC". All that means is there has been some minor design change beyond model '4704383AB", and that one has had a minor change since the model "4704383AA" came off the assembly line. This applies to sensors, fenders, carpet, power window switches, and every other part that is on the vehicle. For your Engine Computer, it started out as part number "56044536AA". Many design changes took place before your computer was even built. Chances are it came off the assembly line with the part number "56044536AD". Once one of the engineers decided to make an improvement, the software update was made available to the dealers' mechanics, and you might have gotten a recall notice in the mail. That applies to emissions and safety issues. If it was merely a customer satisfaction concern, only a service bulletin is provided to the mechanics so they are aware of the availability of updated software and the condition is addresses. If that update is installed, the mechanic puts a new sticker over the original label, with the new part number, so others in the future will know that update has been done.