I thought they just renamed it years ago. Somebody said 9+ was like moose milk. Seems like I used to buy 9+ back in the 80's and it was the same tan stuff that is sold now with the Kerosene in it.
Here is what Google AI has to say if it is worth anything. Some of it doesn't make sense though.
Bob
Search Labs | AI Overview
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Hoppe's No. 9 Plus and Hoppe's Black Powder solvent are both gun cleaners, but No. 9 Plus is designed specifically for black powder shooters. No. 9 Plus lubricates while it cleans, while Black Powder solvent is a cleaning solvent only. Here's how they compare:
Purpose
No. 9 Plus is a patch lubricant and solvent for black powder, while Black Powder solvent is a cleaning solvent for general firearm use.
Properties
No. 9 Plus protects against rust and corrosion, and some say it smells like Hoppes #9 but not as strong. Black Powder solvent is a strong rust inhibitor and helps prevent carbon and lead buildup.
Use
No. 9 Plus cleans fouling from bores and lubricates. Black Powder solvent cleans fouling and loosens dirt from firearm parts.
Barrels
No. 9 Plus works for both shallow and deep grooved barrels. Black Powder solvent is for general firearm use.