The plural of ERP is ERPs. Not ERP’s. The apostrophe doesn’t belong there. The same goes for VPNs, EMTs, HMOs, MCOs, IPOs and WTFs.
But save that apostrophe for when when you talk about what your ERP or VPN can do.
“I’d like to describe our VPN’s features, and our ERP’s capabilities.”
That’s not the plural, it’s the possessive. Meaning that it is your VPN, and you can’t stand people messing with it.
You will also need that apostrophe when you refer to plurals of lowercase letters or numbers.
“Before you send that contract, be sure to cross all your t’s, and dot your i’s.”
Without those apostrophes, your warning would come out, “cross your ts and dot your is.” Which could be painful, I think.
Although when speaking of multiple numerals, leave the apostrophe in your pocket. Why? Because there is no chance for misinterpretation, and besides the pecksniffs say so.
“We are getting way too many 3s on our customer satisfaction reports. We should be getting more 5s.”
Too many Joneses
If you have three people in your department named Charles, you have three Charleses. Yes, it’s ugly, but it’s not the Charleses’ fault. It’s the boss’s fault for hiring three people with the same name.
If just one of those Charleses gave a presentation, you would say “Geez, did you you see Charles’s lame PowerPoint?”
But, if both of them teamed up on a proposal, you would say — and I swear this is correct — “Charles and Charles’s proposal.” Or, “the Charleses’ stupid idea.” Which is precisely why you need diversity in hiring.
Some words are already technically plural, although you sound like a pedant if you treat them as such.
“The media are all over our butts about this silly scandal.”
“The data aren’t wrong. They are just inaccurate.”
If you are a guy and graduated from a college, you are an alumnus of that school. You and your roommates (if they graduated) are alumni.
If you are not a guy and graduated from college, you are an alumna. In a group, you and your cohorts would be alumnae of that institution. Do not peg yourself as ignorant by saying alumina, which is merely an oxide of aluminum found in bauxite.
I find it safer to talk about one thing at a time.