Just to be a little more specific, (BTW, the information you seek can be found elsewhere with the threads of this board... But, I'll cover it here, so you don't have to go hunting)...RULE 1:
Once a Scout "begins" working on a Merit Badge, the current requirements (at that time) may be used until he completes the badge or turns 18, which ever comes first.RULE 2:
Now, here's where is gets messy... Once "revised" requirements are officially released, they may be used in lieu of the "outgoing" requirements. However, a Scout may, at his option, start the MB using either set of requirements until the new MB pahmplet has been updated. Once the MB phamplet has been updated, the old requirements are officially dead (except to those who have already started) and, at this point, a Scout can no longer BEGIN working on the MB under the old requirements. If you are confused, try looking at it this way... The logic behind all this is simple... Even though a Scout (or MBC) knows that new requirements have been released and that the MB phamplet is under revision, he has the right to choose... A) He may BEGIN working on the MB using the "new" requirements or, B) he may BEGIN by using the "old" requirements (but, still current edition of MB phamplet) until the "revised" MB phamplet is published.RULE 3:
Whenever requirements do change, and a Scout has already started on the MB under the old requirements, he always has the option to complete the Merit Badge under the new requirements. BUT, regardless of his choice, the Scout must complete one set of requirements -or- the other... old requirements cannot be mixed and matched up with some of the new requirements, or vice versa, to complete any MB.
Follow those three rules, in order, and you can't go wrong. Should RULE No. "2" it ever become an issue, and I've never seen it happen, the way check is to verify the date of the SM's or ASM's signature on the Blue Card acknowledging the MB is being started, must be BEFORE the MB phamplet's revision date. Besides, if I ever had a doubt, it would be under Rule No. "3" -- mixing and matching requirements.
Are you thoroughly confused, now?