Karen,
The reality of your issue is that it will only become an issue if someone wants to legally challenge something the Board did based on failure to follow procedures.
If this happens, then the Board will need to prove that they did indeed deliver any notices in accordance with your bylaws. I suspect that a signed statement from the individual delivering the items and their appearance in court would be enough proof (providing your bylaws allow for hand delivery).
For proof by the U.S. mail, we purchase the number of stamps needed for the mailing and send one of those letters back to the association. We then clip the receipt for the stamps to the unopened letter sent back to the Association and keep it as an attachment to the minutes as part of our proof of notice. The other option would be via certified mail.
Proof of delivery is not the same as proof of receipt.
We had one person who refuses to pick up certified mail from the Association. In these cases, we would send one letter via certified mail and one letter via first class mail. This fact would be stated within the letter being sent. This helped to prevent the person from saying that they were unaware of what was in the letter because they never picked it up from the post office.
For your specific issue, you need to look at what the law requires, as well as your own governing documents (as they can be more restrictive then the law).
Per
Washington nonprofit corporation act, RCW 24.03.080 Notice of members' meetings, "If notice is provided in a tangible medium, it may be transmitted by: Mail, private carrier, or personal delivery; telegraph or teletype; or telephone, wire, or wireless equipment that transmits a facsimile of the notice. If mailed, such notice shall be deemed to be delivered when deposited in the United States mail addressed to the member at his or her address as it appears on the records of the corporation, with postage thereon prepaid. Other forms of notice in a tangible medium described in this subsection are effective when received."
Note: Tangible medium = a writing, copy of a writing, facsimile, or a physical reproduction, each on paper or on other tangible material.
If I was on your board, since the homeowner stated "I've been advised that mail taped on a door is not considered legally delivered/received", I would have asked her for the proof (section of law, court case, etc.) that supports this advice and, once received, the Board will consider the issue. However, it is the Boards understanding that hand delivery is in compliance with Washington State nonprofit corporation act. In other words, put the burden of proof back on the homeowner while indicating a willingness to change procedures providing proof of her statement can be provided.