What happens when you put a block in AutoCAD?

When you insert a block, AutoCAD looks to see if that block already exists in the current file. If it does, then the software will use the block that is in the file. This is a good thing, as it keeps you from messing up blocks in your file that you have customized.
For More Information Please Refer:
https://cadtips.cadalyst.com/edit-blocks/massively-redefine-all-blocks-drawing
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