Corey Rockwell is a PRO official that has worked in MLS for several years. He is also on Twitter, and recently he mentioned that MLS had a new interpretation to offside which will go into effect in 2015 (Updated to Reflect Explanations by Rockwell). I'll let Corey's tweets explain:

Offside interpretation changes upcoming for #MLS in 2015.

— Corey Rockwell (@coreyrock) February 1, 2015

More emphasis this year on offside players "impacting the ability" of the defense to make a play.

— Corey Rockwell (@coreyrock) February 1, 2015

Therefore, goals that counted in 2014 would be considered offside in 2015.

— Corey Rockwell (@coreyrock) February 1, 2015

If you look at the PRO plays of the week from last year concerning offside, several were correctly onside for '14 but are offside for 2015.

— Corey Rockwell (@coreyrock) February 1, 2015

So in terms of going from some of the plays of the week that PRO mentioned last year, should this be whistled for offside now? (Update: Yep, as explained below)

New offside interpretation (final). In this example, @magee9 would be considered offside in 2015 http://t.co/paG8g1oXhr

— Corey Rockwell (@coreyrock) February 1, 2015

Or perhaps this, Chris Rolfe's goal vs. Philadelphia last year?

Or this goal from Seattle-Chivas? (Update: Yep, would be offsides, as explained below:)

New offside interpretation (pt 1) In video, Neagle does not touch the ball and @1DanKennedy is not interfered with. http://t.co/23CenDiwjL

— Corey Rockwell (@coreyrock) February 1, 2015

New offside interpretation (pt 2) Therefore, in 2014, I correctly let this go and this would be considered onside.

— Corey Rockwell (@coreyrock) February 1, 2015

New offside interpretation (pt 3) At the :15 mark, Neagle makes a slight "flinch" in a slight attempt to play the ball.

— Corey Rockwell (@coreyrock) February 1, 2015

New offside interpretation (pt 4) This flinch "IMPACTS THE ABILITY" of @1DanKennedy to make a play on the ball.

— Corey Rockwell (@coreyrock) February 1, 2015

New offside interpretation (pt 5). According to 2015 FIFA interpretation, this flinch is now considered involvement is offsdie.

— Corey Rockwell (@coreyrock) February 1, 2015

Or this chance from Round 1 of D.C. United vs. the New York Red Bulls?

In terms of interpretations, MLS was tasked with a similar edict in 2014 when it came to holding and/or dragging down attackers in the box on corner kicks (it happened three times that I know of, notably in Week 1 with D.C. United), so I would imagine that there may be similar points of contention in MLS games in 2015, so putting it on the radar.

Tangentially, it also should be noted (at least according to Rockwell), that this is a FIFA interpretation, one that UEFA's officials are aware of and should be exercising.