Please elaborate.  Where might we find this requirement?

You might start with J1.2(1).
The rue change is located at L2.
The NOR is the contract that allows competitors to decide whether to sail, how to prepare, and what to bring.
A rule change in the SI is too late for competitors to make those decisions.
Organizing Authorities need to recognize the requirements of pandemic.
The rule writers did not have that opportunity.

I'm not sure I'm understanding your assertion.  Are you suggesting something other than the NOR should state where the ONB can be found?  I"m not sure running an entirely paperless regatta requires anything other than an indication in the NOR where the ONB is located.  But just like any regatta, it's also helpful, but not required, to indicate where the competitors can find a protest form and race results.  Am I missing something?

Nope, I am not.
We agree that it must be in the NOR.

To the OA that goes completely digital, if band width becomes insufficient, or a system crashes, or there is a power failure, what is your back up plan?  Also, remember that foreign competitors and or officials face large premiums and or cannot access US phone / data systems.  WiFi within the club must be adequate.

Nothing in J1 addresses the “notice board”. While it is courtesy to provide this in the NoR, it is definitely not a requirement. Specifically J2.1(10) indicates that this shall be in the SI unless in the NoR. So again, while a courtesy I’d certainly encourage, telling competitors that the notice board is electronic (found at a website) in the SI only meets the requirements of the appendix. 

Eric, it depends on whether you believe the documents are meant to serve you, or to provide the competitors with the information they need to compete fairly and competently.

Philip
I totally agree with you that information such as an “electronic only” notice board “should” be included in the NoR, I disagree with your assertion that it “shall” be included in the NoR. Having an online notice board is not a rule change it just isn’t something most OAs are going to look at if they follow J1. 

But, it is important to separate what is a best practice or something as an OA rep or PRO involved early on in the Regatta planning that we should do and what the rules say we shall do. 

Sometimes situations change (as with covid-19) between publishing a NoR and publishing the SI. Lately OAs are just scrambling to make an event happen at all within the confines of imprecise and ever changing local orders and uncertainty. 

Thanks to The Annapolis Yacht Club pushing this yeas ago, The Sailing World NOOD Regattas have been using electronic notice boards for years now with no problems.  In the NOR and the SI we state that the Official Notice Board will be located online at : http://....... and we list the address to the site.  

"Best practice." 
"Should do."
Or, as I opined, "must."
Eric "ought to" scan my original offering for the word "shall."
I do not write rules. I offer observations and suggestions. As do we all.
Some of mine have been adopted in the RRS.

J2.1 The sailing instructions shall include the following information:
......
(10) unless stated in the notice of race, location(s) of official notice
board(s) or address of online notice board.

Sorry Eric - you had already pointed this out.  

Well, J2.1 "shall" indicate the official notice board it's a mandatory practice as to be sure competitors know where to look.
But stating in a website or whatsapp or whatever platform that the SI are in the website or whatsapp or whatever, is like to say on your radio, on channel 72, that "all official notice will be transmitted on channel 72". Who's going to listen to you, unless ALREADY on channel 72?

So either the SI publication system is clear on NOR, BEFORE people get to the site (as also to be properly equipped, with smarphones or tablets or whatever necessary); failing this, it's easly  to consider that as an improper action of the RC and boats can get a redress.