Even if it were being used without permission, the fact that it could be used at all in 1911 suggests that it is too old to be covered by copyright, doesn't it?
Otherwise those guys back in 1911 will go back in time and undo what they've done, because it was clearly not worth it.
Back in the real world, modern copyright is pretty messed up.
A work is considered to have been copyrighted before 1923 if it was published:
* in an authorized publication
* in the United States
* before 1923
* and had a proper copyright notice
The sticking point here is that the purported owners of the copyright claim that the 1911 publication of Happy Birthday to You was unauthorized. Therefore, since the first authorized publication was in 1935, the copyright should run from that date.
http://blog.librarylaw.com/librarylaw/2009/07/the-myth-of-th...
https://copyright.cornell.edu/resources/publicdomain.cfm
It clearly states that all works from before 1923 are all in the public domain.
http://www.infotoday.com/searcher/sep12/Hirtle--When-Is-1923...
On this page, in section 4, "The myth of the pre-1923 public domain", there is an explanation about authorized publication:
"For publication to have occurred, the work must be issued with the authorization of the copyright owner. A “pirated” copy of a work published in 1922 without the copyright owner’s authorization is, for the purpose of copyright, considered to be unpublished. If a copyright owner subsequently authorized publication in, say, 1970, the work received a 95- year term starting on that date. Reproducing or otherwise using the 1922 work in a way that implicates one of the rights of copyright would infringe on the copyrights established by authorized publication in 1970."
It goes on to specifically reference Happy Birthday to You as an example of this principle.