Do you actually mean backdating: standing now in 2014 and saying 'ooh in 2010 I did x I think that will count for phase 1 in octant z'
do you mean just taking several years to complete an octant: standing in 2010, you actually completed x for octant z, and now standing in 2014 you have gone and completed y for phase 3 of octant z?
There's nothing wrong with spreading out your completion of Look Wider over your entire time in Senior Section, if you so choose, as long as what you are doing is a challenge to you at the time you complete it. There's no time limit on how long you take to complete individual octants or the chief guide's challenge (other than before your 26th birthday obviously).
Although you've used the phrase 'backdating', from the way you've worded your actual question I'm not sure if you are actually asking if you can look back and add things after the fact? (i.e. backdating) If you are, the answer is, it depends whether you were in TSS at the time and whether it met the rules for LW (ie challenged you sufficiently and appropriately for the phase, hours, wasn't for school/college, etc).
Sorry for the bad wording. I meant that I started recording what I have been doing in 2010 and completed phase 1 and 2 but I didn't finish phase3 until 2014. I was told today everything has to be within two years of completing the octant. i.e. only things from 2012 to 2014 would count towards my octant?
There is no two year rule for Look Wider. You can count anything you have done between 14-26, assuming you were a member of Girlguiding at the time. A lot of people would never complete them if you had to do everything in one octant in 2 years.