Minecraft Version: 1.12.2
Forge Version: 2611
Mod Version: 1.6.5

The following rule causes all instances of "minecraft:stone" to drop "minecraft:stone:1":

{
	"match": {
		"blocks": {
			"blocks": ["minecraft:stone:2"]
		}
	},
	"replaceStrategy": REPLACE_ALL_IF_SELECTED,
	"drops": [
		{
			"selector": {
				"silktouch": EXCLUDED
			},
			"item": {
				"items": ["minecraft:stone:1"]
			}
		}
	]
}

It works fine for me.

I broke many stone blocks and got the expected results. I recorded the debug output of breaking minecraft:stone:3 and minecraft:stone:2.

Here is the script I used to test: issue10.json
Here is the debug log output: log output

Are you testing this with only the Dropt mod installed or are there other mods installed?

Can you enable the debug output and post a link to your debug output? Please use gist or pastebin and link to that.

Ok, I think I reproduced what you might be experiencing.

I noticed this in the log: https://gist.github.com/codetaylor/c4a580648ec37b9c972f43b0eb87bbe7#file-gistfile1-txt-L18

It should only be matching against meta 2, but it's also matching against meta 0.

I tested the same JSON and when mining minecraft:stone:0, the result was minecraft:stone:1.

I'm pretty sure I've found the problem and I'm fixing and testing it now.

Fixed in 1.12.2-1.6.6.

Thanks for reporting this!