The FAR referenced, as stated, is applicable only to dispatch. To determine tha actual runway available for landing, Landing Distance Available (LDA), you need to look at the back of the 10-9 page. For the given runway there may be a number next the the published distance after glideslope. If this number is published then this is the legal LDA. If no number is in the column, then the LDA is the published runway length. Typically, Boeing will publish stopping distances that include touchdown 1000' down the runway. The glideslope may take you farther down the runway depending on GP angle. It seems your company has looked at both cases depending on approach type.