So I take it reading comprehension is not a strong suit. Let's review:
statement #1 on MGL 140-123:
Dealer cannot sell large capacity mag, true. That said, the statute says nothing about manufacturing a non-large capacity mag, does it? A dealer can manufacture and sell non-large capacity magazines if licensed so. A dealer can manufacture them from anything, including large capacity mag components as long as the end result IS a non-large capacity magazine. Now, you may argue that a person could potentially reverse the mag to make it large capacity. As with adding a +5 extension to a 10-round Glock mag that you bought at BassPro: modifying magazines to make them large capacity IS illegal but DOES NOT implicate the seller/dealer in the crime.
I can even take it a step further. Let's say a bad guy buys a 10-round mag, replaces the body with a 3D printed longer version capable of accepting 11 rounds. He keeps the original spring, follower and base plate. Should the dealer that sold him a 10-round mag be now responsible to?
But let's continue reading your quotes:
Where in the above sentence do you see ANYTHING about magazines? the entire MGL 140-128 talks about punishment, NOT the legality of feeding devices.
Find better quotes next time. Better yet, read them before you post.