Apprentice and trainee data are reported by the State and Territory Training Authorities to NCVER on a quarterly basis, starting at the September quarter of 1994. The set of data submitted that quarter is referred to as Collection 1. The sets of data submitted in subsequent quarters are referred to as Collection 2, Collection 3 and so on. NCVER publishes data on the numbers of contracts of training that commence, complete, cancel/withdraw, re-commence, expire or are suspended and the time at which these events occur (referred to as the "date of effect"). From these events, the number of contracts in training at a given time can be calculated. Due to time delays in reporting data on the status of contracts to NCVER, the most recent data are estimated. In short, the estimation methodology is based on the calculation of "average lag ratios". A lag ratio is the ratio of the actual number of events (commencements, completions, etc) which occurred in a particular quarter to the number of those events which were reported in a given quarter. The average lag ratio is calculated by taking the average of the lag ratios found in a "time window", which is a moving period of eight quarters from the past. Further details on this methodology are provided in the technical paper produced by NCVER, Estimation of apprentice and trainee statistics, which may be found on the NCVER Portal as a related item to this quarterly publication. The purpose of this technical paper is to document the adjustments that are made to the estimates at each collection, and produce a cumulative document of these adjustments, commencing at Collection 87, March 2016 estimates. [For "Australian Vocational Education and Training Statistics: Apprentices and Trainees 2016--September Quarter," see ED573503. To access "Apprentices and Trainees: Terms and Definitions. Support Document," see ED573505.]