This follows on from Contour Markings (Gape Darts).
The Sleeveless Bodice Block is a deritative block; it is created from the Bodice (Sleeves) Block, with a few changes made. Like all derivative blocks, it is not essential; you could just use the Bodice (Sleeves) Block and make the changes each time you make a sleeveless garment.
Creating a Sleeveless Block saves having to reduce the block and armhole ease each and every time you make a sleeveless pattern. While it might not sound much, if you make a lot of Sleeveless garments, it is worth the effort.
Below find a few images that show you the difference between the two blocks.
Bodice Front with Contour Markings: Sleeves & Sleeveless
Figure 1 shows the Bodice Front with Countour Markings: the contour markings No.1 & No.2. (reducing the ease at the underarm level of the garment, and the armhole ease) that are shown on the Bodice Front (sleeves) do not appear on the Sleeveless Block because those changes have been incorporated into the block. These two changes are necessary for all sleeveless garments. The other possible changes (indicated by the contour markings) may or may not be required depending on the design.
Bodice Back with Contour Markings: Sleeves & Sleeveless
Figure 2 shows the Bodice Back (sleeves) compared to the Sleeveless Bodice Back: the contour mark reducing the underam ease (indicated by No.1) in the Bodice (Sleeves) has been incorporated into the Sleeveless Block
Comparison Bodice (Sleeves) and Sleeveless Bodice
Figure 3: The Bodice (Sleeves) and Sleeveless Bodice have been superimposed for comparison.
Continued in Standard Contouring Amounts.