To change the Working Date - Left click on the Date in upper right hand corner of project screen. This will give you the opportunity to change the date to anything. Use 12/31/2100 per my suggestion from previous post. Inventory values are as of all time. So if we make an adjustment to supplies using the current date, supplies used in new farming operations (even when using a past date) will use the cost/qty from current. However, there may be adjustments made accidently in the future, thus why I was asking for you to see what would be showing in inventory based upon a futures date.
You can zero inventory items and reuse the same inventory again. I recommend that you make adjustments using the current dates. I was afraid you had duplicate supplies causing your problem, based upon your first post. I am not telling you to retired supplies that you want to keep using, only if you have duplications.