It is a little confusing. We originally bought 59 tanks to equip the tank force we had at the time - a regiment of two squadrons. The number was actually quite generous for that - 30 or so for the regiment (two squadrons of 14 and two HQ tanks) about a dozen for the school of armour and a couple for the logistic school for training, which left a dozen or so 'spare' tanks which are for attrition and to allow maintenance etc to be carried out without impacting the operational fleet.
However, under Beersheeba we now want three 14 tanks squadrons. Maths will tell you the numbers we have now are theoretically enough - 42 tanks in the squadrons, a dozen for the school of armour and a couple for the logistic school adds up to less than 59. However, with no spare tanks it means that the squadrons will never be able to put 14 tanks in the field - a few will always be in maintenance, being upgraded etc. The only way to get around this would be to rotate tanks, moving them between the regiments as part of the force generation cycle to ensure the ready and readying regiments can put a full compliment in the field. Obviously, this is expensive and difficult.
Buying another dozen or so tanks allows for that attrition. Each squadron could be allocated 18 or so tanks, to ensure they always have enough serviceable tanks to put 14 in the field at once. This is what army is seeking to occur. However, government hasn't agreed to it yet. If the government does agree to this, and I reckon they will as it's pretty cheap in the grand scheme of things, it will probably happen as part of the White paper process.