The one KEY tip from ECHA for this registration deadine is ensuring the identity of the substance is the same as those of other pre-registrants. The ECHA guidance document on substance identification is quite extensive and the job of identifiying the substance for registration should ideally be undertaken by Industry experts. One of the key elements is how to name the substance and identifying the same substances is  particularly important for in the process of (late) pre-registration of phase-in substances, for inquiries, for data sharing, for Joint Submission of data. The guidance is available on the ECHA website at the following link. http://echa.europa.eu/documents/10162/13643/substance_id_en.pdf