You did mention that a single sync point is already in use at resolutions above 1 day. I think we're starting to confuse ourselves though... we should consider the system as a whole... if MCFX uses one supra-daily sync point AND one daily session sync point then we have a system that uses two synchronization thresholds to synchronize charts - not a single sync point system as you proposed.
Let's try to drop the jargon, because I think it's leading to misunderstanding.
MCFX currently appears to use two completely separate methods of ensuring its time-based charts are synchronised with one another - one method for n-day charts, and one for n-hour, n-minute, n-second, n-tick. I exclude discussion of n-week, n-month etc. charts: they don't interest me for the moment.
In general, all that's necessary for time-based charts to be correctly synchronised - by which I mean that all bars of a given time scale open and close together, and all multiples and fractions of that time scale correspond as they should, is to choose one arbitrary moment in time, and ensure that all charts in all time scales break their bars together at that time. That moment could be 12 noon on Christmas day 1987, or it could be (more practically) NY close this Friday. Once that unique point of synchronisation is defined, simple arithmetic will take care of the rest.
For example, if I define my one fixed point as "now", then I can divide up the future and the past arbitrarily into equal parcels of time, backwards and forwards to infinity, and any data tick that will occur or has occurred inside any of these parcels contributes to the candle that corresponds to that parcel. As long as the criteria of the candles are respected, and assuming no cumulative errors in the data stream, the simple correspondence of arithmetic will ensure that synchronisation occurs between time scales that are co-factors, and no candlesticks are ever broken before their time. Two 3-hour candlesticks will make a 6-hour candlestick, and every time a 12-hour candlestick opens, a 6-hour, a 3-hour, a 90-minute, a 45-minute, a 15-minute, and a 5-minute candlestick will open. A 10-hour candlestick break and a 12-hour candlestick break will coincide every 60 hours, but when a 10-hour candlestick opens, a 5-hour candlestick will open at the same moment.
That's the method the n-day charts use. The arbitrary fixed point is the end of the current trading week. Creating an n-day chart causes time to be divided up into n-day parcels streaming back from that point. An m-day chart likewise, m-day parcels. n-day and m-day charts will correspond at any point at which n and m are both factors, i.e. multiples of their lowest common multiple. To use my example from the other day, 17 and 23-day bars will correspond naturally every 391 days - no more, no less.
The second method is used by all the sub-daily time scales. That method is to divide the trading day up according to the bar critieria, but any bar open at NY Close is broken at NY Close, and a new day (and hence a new bar) begins.
If n-day charts used this method, there could be no value of n greater than 1.
All I'm suggesting is that there need be no arbitrary candlestick breakage. If all time scales are managed as the n-day charts are currently managed, using one unique, arbitrary synchronisation point (the end of the current week, for example) those charts which correspond naturally (e.g. 1,2,4,8,12,24h charts) will continue to do so. Those which are currently useless due to broken candles (e.g. 10h, 16h) will correspond naturally to those other time scales with which they have common factors mathematically, with no broken candles.
There may be a need for error checking, depending on how the data stream is supplied, but that can be done invisibly, and the good accuracy of long n-day charts shows that MCFX is already capable of doing what's necessary.
Apologies if that all seems simplistic, but I just want to be sure we're talking about the same thing.
By the way, what is that supra-daily sync point and are you sure it exists? For instance, how can you be sure that for chart resolutions above 1 day MCFX doesn't just say something like "skip X number of daily sessions before closing the candle"? Plugging in 7 for X would produce a weekly chart.
Essentially that's exactly what does happen, and what should happen. What you call the "supra-daily sync point" is just the one arbitrary moment (the end of the current trading week) at which MCFX decides all candles should line up.
It's clear that such a point exists, because creating a chart that superimposes several different multiday charts (e.g. 13, 17, 23-day) which should only have rare correspondences, the bars are all aligned at the end of the current trading week.
So let me see if I understand this correctly...
1. there are no broken candle issues in resolutions above 1 day
Right, at least not in the n-day charts.
2. MCFX currently uses multiple sync points system-wide
True?
I don't know what you mean by that.