You're on the right track, but let's break down the calculation for a 32-unit multifamily dwelling with 18 kW ranges using NEC 220.55 and its notes, focusing on accuracy and clarity

Understanding the Code (NEC 220.55)
Table 220.55

This table is for calculating the demand load for ranges and ovens in dwelling units.

Column C

This is typically the relevant column for more than 5 ranges but less than 51.

Note 1

This is the crucial part for ranges exceeding 12 kW. It states: "The maximum demand in Column C shall be increased 5 percent for each kilowatt rating above 12 kW."

Step-by-Step Calculation1. Base Demand from Table 220.55

For 32 ranges, Column C indicates a demand of 15 kW. We start with 15kw.2.

Oversized Range Adjustment (Note 1)

Each range is 18 kW - 12 kW = 6 kW above 12 kW. The increase is 5% per kW above 12 kW. So, 6 kW 5% = 30% or 0.3 (as a decimal). Multiply the demand value (15kw) by the percentage increase: 15 kW 0.3 = 4.5 kW.
3.

Adjusted Base Demand for Oversized Ranges

Add the percentage increase to the base demand: 15 kW + 4.5 kW = 19.5 kW4.

Additional Ranges

For each additional range above 1 unit you add 1kw: 31 (additional ranges) x 1 kW = 31 kW 19.5 + 31kw = 50.5kw

Final Demand Calculation50. 5 kW is the demand factor for 32 ranges.

Important Considerations and Clarifications Note 1: "For each kilowatt rating above 12 kW" means the percentage increase is applied to the demand load from Column C, not the additional range calculation. You don't multiply the 1 kW for each additional range by 1.3. You only apply the percentage increase (based on how much each range exceeds 12 kW) to the initial demand load you get from Column C. Understanding the Intent

The code aims to account for the higher potential load of these larger ranges. The percentage increase acknowledges that larger ranges can draw more power.

Consult with a Professional

These calculations can be complex, and it's always best to consult with a qualified electrical engineer or inspector, as local interpretations and specific project requirements can influence the final design.

In summary, your initial approach was very close. The key is understanding that the 5% increase per kW above 12 kW applies to the base demand you find in Column C of Table 220.55, before* adding the 1 kW per additional range. After the increasing the base demand for oversized ranges you would add 1kw per additional range and this does not get affected by the 5% increase. Flag for review