Icefields is a beautiful ride so hopefully it doesn't come to that. However, I'll note that you likely have some flexibility in sorting choices along the way:
1. At both Prince George and Tete Jaune Cache there is both internet and an alternate road heading southbound.
2. You might have flexibility if you needed to delay or shift things by a day.
3. There are multiple choices between campgrounds and hostels so if necessary can make a shorter day or longer day.
So that gives an ability at Prince George to do a second round assessment and look through combination of alternatives, perhaps shifting a day or doing a short hop if necessary. If it looks completely bleak then you can defer finalizing a choice until a few days before.
Alternately you could make some of those duplicate reservations earlier and again not months in advance but a week or two.
In my case in mid-August 2016 it was peak tourist season and I was fortunate in making reservations two days before entering. Things were mostly full and so not everything I tried was available but enough to put together a plan with reservations. I ended up spending a week in Smithers having a hub replaced (including replacement being mailed under warranty) so if I had made reservations much in advance of that, I would have had to change anyways or use the train to skip ahead.
Yeah, I know. I am just for friggin frustrated with Government "efficiency" (and my wife works for them). I get the reason for the need for reservations and even the reason behind the scramble for the first-come, first-served sites. I also see that in the national parks (Canada & US) that cyclists/hikers are not an insignificant number of visitors and that the cyclists/hikers have a legitimate need for accommodations in the form of hiker/biker sites and a "no turn away" policy, especially if the National Parks want to truly 1) reduce the carbon footprint they so fondly talk about, 2) discourage/prevent illegal camping, 3) reduce congestion on the roads, etc. Then when I had the volunteer "Ranger" (don't know title) tell me they shut down 1 of 2 major campgrounds in Zion WHILE they EXPLORE what they are going to do (supposedly nothing major was wrong so an usable, in-demand CG goes empty), just causes me to get frustrated when things are preventable/fixable without much effort or expense.
I had already planned to make reservations sometime after I turn onto BC-16.
The source of all this is the "never do" reason of having a deadline in that my wife is flying out to join me in Columbia Falls so I have to be there on X date. If I didn't have the deadline, I would just show up and go with the flow. I can hopefully build in some extra days between Deadhorse and Jasper enough to still make my deadline. That is probably as I will probably only need an additional day or two "buffer days". If I do, I can always take the longer Waterton/Glacier route versus Eureka route or just take shorter days after I get through the Icefields gauntlet.