Melissa, this is a really thought-provoking question you raise. I think in many cases agencies are planning and assuming that congregations will participate in ministry shares AND will schedule offerings for some of the same causes. Deacons know this, and so they often schedule offerings that give the congregation the opportunity to give "over and above" the ministry share.
As you point out, this can cloud the question of how much a church is actually giving to a given agency or cause.
I think in other cases, deacons are aware that budget short-falls in the church are being addressed by shorting ministry shares. Then offerings might be intended to help meet the congregation's classical and denominational "fair share".
I'm struck by your statement that deacons make the schedule for a year in advance. In my church the offering schedule is made for much shorter intervals, and the deacons view it with a lot of flexibility, depending on a variety of factors.
Along with you, I'm eager to hear of how deacons in other churches think about these questions.






In our congregation the deacons meet in November to set the offering schedule for the following year. Using the deacon's helper resource, sifting through the pile of offering requests received throughout the year and sensing the heart of God in the congregation, they prayerfully discern what causes to support.
This year, a question was raised to our deacon team about the causes they had chosen to support. The question was this: when we as members are already contributing through denominational and classical shares to specific ministries, why are we also designating many of our weekly offerings to these same causes? (The question was not intended to be a slight towards our deacons, but rather was brought forward out of a desire to have transparency in knowing how much we were actually giving where, particularly when we have hesitated to bring on another staff person because of the budget).
I am curious as to how other congregations designate their offering causes. I know location and ties to specific ministries may create variance in answers (ie. a congregation in Grand Rapids supporting Calvin College vs. one in California), however, how do we support well both the denominational family we are part of and the local community we find ourselves active (and desiring to be more active) in?