Since you're using the LGPL, I suggest you follow the GNU project's recommendations: your copyright notices should look like
Copyright © 2013, 2014, 2015, 2016 cannatag
and you should simply update them all at the start of every year, assuming you're publishing every year (if your source code is publicly available during development, that could be construed as counting as publication). The GPL howto clarifies this:
Whichever license you plan to use, the process involves adding two elements to each source file of your program: a copyright notice (such as “Copyright 1999 Terry Jones”), and a statement of copying permission, saying that the program is distributed under the terms of the GNU General Public License (or the Lesser GPL).
The copyright notice should include the year in which you finished preparing the release (so if you finished it in 1998 but didn't post it until 1999, use 1998). You should add the proper year for each release; for example, “Copyright 1998, 1999 Terry Jones” if some versions were finished in 1998 and some were finished in 1999. If several people helped write the code, use all their names.
If you want to play it safe and avoid any accusation of over-reaching in your copyright notices (I have no idea how much of a risk that is), you might instead want to update the years only when you make non-trivial changes to the relevant files; so you'd end up with a variety of copyright notices depending on when each file was edited:
Copyright © 2013, 2015 cannatag
Copyright © 2014, 2016 cannatag
Copyright © 2014, 2015, 2016 cannatag
Other projects have different recommendations; thus the Eclipse Foundation recommends mentioning the first and last year of publication in each file:
Copyright © 2013, 2016 cannatag
Even that is subject to interpretation, and for example in OpenDaylight we use the Eclipse form, per-file: each file has a copyright notice with the year it was created in and the last year it was updated in.
You should avoid ranges though, they don't have a definition in US copyright law at least.
Given the variety of practices out there I can't see the details actually having an impact beyond documentation; when it comes to courts, it seems to me that actual copyright is decided based on more than the notices themselves (see for example Conservancy's analysis of Christoph Hellwig's contributions to the kernel). (Of course I am not a lawyer and you should consult one if this is troubling you.)